Probably one of your parents had some talent, expextations, desires, connected with one of the things that Mecrury rules but they never achieved it or never developed this talent. And now, you have this talent or you make something that one of them wanted but didn't make and this is an activity or talent by Mercury. Is that so?
Ah, now that I thought about it, yes it is true. My mom has a literary talent, she wanted to be a journalist. But then circumstances changed and she became an accountant instead. I think I inherited her talent, along with her love of reading.
However, I am not in the field where I can nuture these talents myself. Though, I am still trying to develop it by having reading and writing as my hobbies.
Also, about the 4th/5th house theory, I think it may quite be true. The 5th house is also the house of creativity, right? I have Pluto, sun and mars there conjunct. Back in my childhood, my father was the one who pushed me to venture into creative activities-- acting, theater, singing.
I have my moon in the 9th conjunct MC and rules the 2nd house. My mother was the helped me find a benefactor for my college education and now currently has a large influence on my career.
Having said all that, I think there is some accuracy to it.